In recent years, in the field of electronic components, resin compositions (for example, sealing agents, solder resist, etc.) for use in the electronic components have been required to have better heat resistance, electrical properties, and moisture resistance in order to deal with reduction in size, reduction in thickness, and increase in speed. Therefore, polyimide resins, polyamideimide resins, and polyamide resins have been used as resins constituting the resin compositions, in place of epoxy resins. However, these resins have a rigid resin structure, and the cured films lack flexibility. Therefore, the case of using the resins for thin film base materials has problems such as significant warpage of the base materials after curing, and poor flexibility.
For the resins mentioned above, in order to improve the warpage behavior and flexibility, it has been also previously considered that the resins are modified to provide flexibility and reduce the elastic modulus, and various types of modified polyamideimide resins have been proposed (see, for example, Patent Literatures 1, 2, and 3).
On the other hand, Patent Literature 4 discloses a thermosetting resin composition which is improved in small warpage behavior, flexibility, solder heat resistance, and tin plating resistance.